Variable-flow high pressure pump

ABSTRACT

A variable-flow high-pressure pump comprising at least one piston mounted to slide axially and in a leak-tight manner within a cylindrical cavity obtained in the body of the pump so as to define a variable-volume pumping chamber adapted to be filled with a fluid, and an intake valve and a delivery valve adapted to enable the one-way flow of the fluid respectively into and out of the pumping chamber, the intake valve being formed by a non-return valve comprising a shutter body which can move to and from a closed position in which it prevents the passage of the fluid via the valve, and an elastic member adapted to maintain the shutter body in the above-mentioned closed position, the high-pressure pump further comprising a hydraulic piston selectively adapted to distance the shutter body from the closed position by overcoming the resistance of the elastic member so as to enable the fluid also to flow freely via the valve in a direction opposite to the normal direction.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a variable-flow high-pressure pump.

[0003] The present invention relates, in particular, to a variable-flow high-pressure pump for diesel engines with a fuel supply system of the common rail type, to which the following description will explicitly refer without entering into general details.

[0004] 2. Background of the Invention

[0005] As is known, the common rail supply system requires the use of a high-pressure pump which is able to supply fuel at very high pressure to a collection container for the pressurized fuel interposed between the high-pressure pump and the fuel injectors, with a variable flow so that the quantity of fuel supplied to the collection container can be regulated in real time as a function of the operating conditions of the engine.

[0006] The high-pressure pumps that are currently known receive the fuel from a low-pressure pump and normally comprise a piston which is mounted in an axially sliding manner within a cylindrical cavity obtained in the body of the pump so as to define a variable-volume pumping chamber adapted to be filled with fuel, and a pair of non-return valves adapted to regulate the flow of fuel from and to the pumping chamber during the variations of the volume of the pumping chamber caused by the alternating movement of the piston within the cylindrical cavity.

[0007] In further detail, the pumping chamber is connected to the pressurized fuel collection container via a first non-return valve oriented so as to enable fuel to flow from the pumping chamber to the collection container, and is connected to the delivery of the low-pressure pump by means of a second non-return valve oriented so as to enable fuel to flow from the low-pressure pump to the pumping chamber.

[0008] The two non-return valves are normally positioned within the body of the pump along the two connection ducts via which the fuel enters and leaves the pumping chamber, and comprise a shutter body mounted in an axially sliding manner within a cylindrical duct obtained along a section of the connection duct, and an elastic member which is disposed within the cylindrical cavity so as to maintain the shutter body in abutment against a sealing seat obtained at the location of one of the two axial ends of the cylindrical cavity, so as to close the opening provided at the location of this opening in a leak-tight manner. The cylindrical cavity is in practice in communication externally via two openings obtained at the location of the two axial ends of this cavity.

[0009] With this arrangement, it is evident that the fuel can flow freely via the cylindrical cavity of the non-return valve only when it penetrates within this cavity via the opening disposed directly facing the shutter body, i.e. when it penetrates within the cavity via the opening adapted to be closed by the shutter body.

[0010] In order to regulate the quantity of fuel supplied to the fuel collection container during each piston stroke, i.e. the rate of flow of the pump, the high-pressure pumps currently known are further provided with a linear electromagnetic actuator able, on command, to interfere with the normal operation of the non-return valve interposed between the pumping chamber and the low-pressure pump, so as to enable the fuel also to flow freely via the valve in a direction opposite to the normal direction.

[0011] In further detail, the output shaft of the linear electromagnetic actuator is able, on command, to counter and maintain the shutter body of the valve raised from its sealing seat, so as to enable the fuel to flow via the cylindrical cavity even when it comes from the opening disposed directly facing the elastic member, i.e. from the opposite portion of the shutter body with respect to this elastic member.

[0012] If the non-return valve disposed at the location of the intake inlet of the pump is kept open when the pumping chamber starts to reduce in volume, it is possible to cause part of the fuel that has previously filled the pumping chamber to flow back again to the low-pressure pump rather than to the pressurized fuel collection container, thereby making it possible accurately to regulate the quantity of fuel supplied to the collection container during the end section of the piston stroke, when the action of the linear electromagnetic actuator ceases and the valve starts to operate normally again.

[0013] Unfortunately, the system for regulating flow by means of the linear electromagnetic actuator is not suited to location in high-pressure pumps provided with two or more pistons: in this case, the high-pressure pump would have to be equipped with a linear electromagnetic actuator for each pumping chamber, with the problems of driving of the actuators and consumption of electrical energy that this entails.

SUMMARY OF INVENTION

[0014] The object of the present invention is therefore to provide a high-pressure pump with a flow regulation system that can also be readily used with pumps provided with two or more pistons.

[0015] The present invention relates to a variable-flow high-pressure pump comprising at least one pumping piston mounted to slide axially and in a leak-tight manner within a cylindrical cavity obtained in the body of the pump so as to define a variable-volume pumping chamber adapted to be filled with a generic fluid, at least one intake valve and a delivery valve adapted to enable the one-way flow of the fluid respectively into and out of the pumping chamber, the intake valve being formed by a non-return valve comprising a shutter body which can move to and from a closed position in which it prevents the passage of the fluid via this valve, the high-pressure pump further comprising flow regulation means adapted to interfere with the normal operation of the intake valve in order to enable the fluid also to flow freely via the valve in a direction opposite to the normal direction, the high-pressure pump being characterized in that the flow regulation means comprise a hydraulic piston selectively adapted to prevent the shutter body from returning to the closed position.

BRIEF DESCRIPTION OF DRAWINGS

[0016] The present invention will be described below with reference to the accompanying drawings, which show a non-limiting embodiment in diagram form.

[0017] In the accompanying FIGURE, a variable-flow high-pressure pump, which may advantageously be used in diesel engines with a fuel supply system of the common rail type, in order to supply fuel at very high pressure to a pressurized fuel collection container interposed between this pump and the fuel injectors (not shown), is shown overall by reference numeral 1.

DETAILED DESCRIPTION

[0018] The pump 1 is provided with a delivery outlet 1 a which, in the embodiment shown, is adapted to be connected to the pressurized fuel collection container, indicated below by reference numeral 2, by means of a first connection duct, and an intake inlet 1 b which, in the embodiment shown, is adapted to be connected to the delivery of a low-pressure pump, indicated below by reference numeral 3, by means of a second connection duct.

[0019] The pressurized fuel collection container 2 and the low-pressure pump 3 are devices that are widely known in the art and are not therefore described in further detail below.

[0020] The high-pressure pump 1 comprises at least one pumping piston 4 mounted to slide axially and in a leak-tight manner in a cylindrical cavity 5 obtained in the body 6 of the pump in order to define a variable-volume pumping chamber 7 adapted to be filled with fuel.

[0021] The pumping piston 4 may move with an alternating movement in the cylindrical cavity 5 between a first operating position, normally called “bottom dead centre”, in which the top of the piston 4 is at the maximum distance from the base of the cylindrical cavity 5 and the volume of the pumping chamber 7 assumes the maximum value, and a second operating position, normally called “top dead centre” in which the top of the piston 4 is at the minimum distance from the base of the cylindrical cavity 5 and the volume of the pumping chamber 7 assumes the minimum value.

[0022] In the accompanying FIGURE, the high-pressure pump 1 is further provided with a pair of non-return valves 8 and 9 which are adapted to regulate the flow of fuel to and from the pumping chamber 7, during the variations of the volume of the chamber caused by the alternating movement of the piston 4 in the cylindrical cavity 5.

[0023] In further detail, the two non-return valves 8 and 9 are disposed along the connection ducts which bring the pumping chamber 7 into communication with the delivery outlet 1 a and the intake inlet 1 b respectively of the pump 1, and are oriented such that the non-return valve 8 disposed along the duct that ends at the location of the delivery outlet 1 a—also called the delivery valve—can enable the fuel to flow solely as output from the pumping chamber 7, while the non-return valve 9 disposed along the duct that ends at the location of the intake inlet 1 b—also known as the intake valve—can enable the fuel to flow solely as input into the pumping chamber 7.

[0024] In other words, the delivery valve 8 enables the fuel to flow solely from the pumping chamber 7 to the collection container 2, while the intake valve 9 enables the fuel to flow solely from the low-pressure pump 3 to the pumping chamber 7.

[0025] The non-return valves 8 and 9 are substantially of known type, and comprise a shutter body 10 preferably, but not necessarily, of spherical shape which is mounted in an axially sliding manner in a cylindrical cavity 11 obtained along a section of the connection duct leading to the intake inlet 1 b or the delivery outlet 1 a of the pump 1. The cylindrical cavity 11 is obviously in communication with the exterior via two openings obtained at the location of the two axial ends of this cavity.

[0026] The non-return valves 8 and 9 are further provided with an elastic member 12 adapted to maintain the shutter body 10 in a closed position, in which it is disposed in abutment against a sealing seat obtained at the location of one of the two axial ends of the cylindrical cavity 11, so as to close the opening present at that point in a leak-tight manner.

[0027] In the embodiment shown, the elastic member 12 is in particular formed by a helical spring 12 disposed coaxially with the axis of the cylindrical cavity 11 so as to have a first end in abutment against the shutter body 10 and a second end in abutment against one of the two axial ends of the cylindrical cavity 11.

[0028] It will be appreciated that such a constructional geometry allows the fuel to flow via the non-return valve 8, 9 only when it penetrates within the cylindrical cavity 11 of the valve via the opening which is normally closed by the shutter body 10, overcoming the thrust of the elastic member 12. In this case, the pressure difference between the two sides of the shutter body 10 is able to overcome the resistant force of the elastic member 12, distancing the shutter body 10 from its closed position.

[0029] In the opposite case, however, the pressure difference between the two sides of the shutter body 10 is added to the resistant force of the elastic member 12 in order to maintain the shutter body 10 even more firmly in the closed position.

[0030] In a different embodiment which is not shown, the non-return valves 8 and 9 are not provided with the elastic member 12, and the axial displacement of the shutter body 10 to or from the above-mentioned closed position takes place exclusively as a result of the pressure difference which is established between the two sides of the shutter body 10 when the fuel flows via the cylindrical cavity 11 of the valve.

[0031] With reference to the accompanying FIGURE, the high-pressure pump 1 is lastly provided with a flow regulation device 13 for the pump, which is able to interfere, on command, with the normal operation of the intake valve 9, in order also to enable the fuel to flow freely via this valve in a direction opposite to the normal direction, so as to be able to regulate the quantity of fuel supplied to the delivery outlet 1 a during the return stroke of the piston 4 towards the top dead centre.

[0032] The flow regulation device 13 comprises a single-acting hydraulic piston 14 which is adapted to be supplied by a pressurized fluid advantageously formed by part of the fuel from the low-pressure pump 2, and is able axially to displace the shutter body 10 within the cylindrical cavity 11 so as to distance it from the closed position, thereby enabling the free passage of the fuel via the non-return valve 9.

[0033] In order to control the hydraulic piston 14, the flow regulation device 13 further comprises an electrically actuated exhaust valve 15 which is selectively adapted to cause a pressure drop in the fluid supplied to the hydraulic piston 14, i.e. the fuel from the low-pressure pump 3, so as to prevent any displacement of the hydraulic piston 14, and an electronic control unit 16 adapted to drive the exhaust valve 15 so as to control, in real time, the time interval in which the intake valve 9 is disabled in order to be able to regulate the quantity of fuel newly supplied to the delivery outlet 1 a during the return stroke of the piston 4 to the top dead centre and, therefore, the quantity of fuel supplied to the collection container 2 during each stroke of the piston 4.

[0034] In the embodiment, the hydraulic piston 14 is in particular provided with an output shaft 14 a which is adapted to be disposed with its point in abutment against the shutter body 10, and then axially to displace the shutter body 10 within the cylindrical cavity 11 so as to prevent the shutter body 10 from returning to its closed position so as to enable the free passage of the fuel via the cylindrical cavity 11 of the valve. In this case, the output shaft 14 a of the hydraulic piston 14 extends coaxially to the longitudinal axis of the cylindrical cavity 11, from the opposite side of the elastic member 12 with respect to the shutter body 10, and can move axially between a retracted position and a forward position in which it is able to lock the shutter body remote from its closed position.

[0035] The exhaust valve 15 is, however, positioned in a branched manner along a connection duct 17 which carries the fuel from the low-pressure pump 3 to the hydraulic piston 14 so as to be able, on command, to bring the duct 17 into direct communication with the fuel recycling circuit 18 which connects, in a known manner, the delivery of the low-pressure pump 3 with the fuel tank 19 of the vehicle via the interposition of a non-return valve 20 of known type.

[0036] In further detail, the non-return valve 20 is adapted to divert the excess delivery from the low-pressure pump 3 again upstream of the intake inlet of the low-pressure pump 3, and is oriented so as to enable the fuel to flow in one direction from the delivery of the low-pressure pump 3 to the fuel tank 19 and not vice versa, causing a pressure drop of a predetermined value, and the exhaust valve 15 is able to bring the duct 17 into direct communication with the fuel recycling circuit 18 immediately downstream of this non-return valve 20.

[0037] In the embodiment shown, the high-pressure pump 1 is provided with a second non-return valve 21, disposed along the connection duct 17 that carries the fuel from the low-pressure pump 3 to the hydraulic piston 14, and with a throttle valve 22 disposed immediately upstream of the intake inlet 1 b of the pump 1.

[0038] The non-return valve 21 is positioned upstream of the point at which the exhaust valve 15 is inserted on the duct 17 and is oriented so as to enable the fuel to flow from the delivery of the low-pressure pump 3 to the hydraulic piston 14 and the exhaust valve 15, causing a pressure drop of a predetermined value; while the throttle valve 22 is adapted to cause a pressure drop of predetermined value in the pressurized fuel that is flowing to the intake inlet 1 b of the pump.

[0039] The operation of the high-pressure pump 1 will now be described, assuming that the piston 4 is initially at the top dead centre and that the exhaust valve 15 is closed, thus enabling the pressurized fuel to reach the hydraulic piston 14.

[0040] When the descent of the piston 4 to the bottom dead centre commences, the intake valve 9 opens as a result of the pressure difference and the fuel starts to flow into the pumping chamber 7 of the pump 1.

[0041] When the piston 4 reaches the bottom dead centre and inverts its stroke, the pumping chamber 7 starts to reduce its volume, forcing the fuel (fluid and therefore incompressible) out of this chamber again.

[0042] At this point, however, the intake valve 9 tends to close so as to force the fuel to flow out of the pumping chamber 7 via the delivery valve 8, but the output shaft 14 a of the hydraulic piston 14 prevents the shutter body 10 from returning to its closed position, as a result of which the fuel starts to emerge from the pumping chamber 7 via the intake valve 9. At this stage, the hydraulic piston 14 is still supplied with pressurized fuel from the low-pressure pump 3 and its output shaft 14 a is thus in the forward position, preventing the shutter body 10 from returning to the closed position.

[0043] It will also be appreciated that, at this stage, the pressure of the fuel in the pumping chamber 7 is not sufficient to open the delivery valve 8 of the pump, as a result of which the fuel cannot in any way flow to the pressurized fuel collection container 2.

[0044] The drawing of the fuel via the intake valve 9 continues during the upward stroke of the piston 4, until the quantity of fuel contained in the pumping chamber 7 has reached the desired value. At this point, the electronic control unit 16 actuates the exhaust valve 15 so as to discharge the pressurized fuel contained in the hydraulic piston 14, enabling the shutter body 10 of the intake valve 8 to return to its closed position under the thrust of the elastic member 12 and the pressure difference that is established on both sides of the shutter body 10 during the passage of the fuel.

[0045] As soon as the action of the hydraulic piston 14 ceases, the intake valve 9 closes and the fuel pressure in the pumping chamber 7 rises until it reaches a sufficiently high value to cause the opening of the delivery valve 8 and the resultant discharge of the fuel to the pressurized fuel collection container 2.

[0046] The advantages of the high-pressure pump 1 described and illustrated above are evident: an exhaust valve 15 has a consumption of electric current which is substantially lower than that of the linear electromagnetic actuators currently used.

[0047] A further advantage of the high-pressure pump 1 is that a single exhaust valve 15 can simultaneously control one or more hydraulic pistons 14, greatly simplifying the construction of variable-flow high-pressure pumps equipped with a plurality of pumping members.

[0048] It will also be appreciated that the high-pressure pump 1 runs counter to the current constructional trends which impose, wherever possible, the use of linear electromagnetic actuators as a replacement for any other type of hydraulic linear actuator and the like.

[0049] It will lastly be appreciated that modifications and variations may be made to the high-pressure pump 1 as described and illustrated above without thereby departing from the scope of the present invention. 

1. A variable-flow high-pressure pump (1) comprising at least one pumping piston (4) mounted to slide axially and in a leak-tight manner within a cylindrical cavity (5) obtained in the body (6) of the pump so as to define a variable-volume pumping chamber (7) adapted to be filled with a generic fluid, at least one intake valve (9) and a delivery valve (8) adapted to enable the one-way flow of the fluid respectively into and out of the pumping chamber (7), the intake valve (9) being formed by a non-return valve (9) comprising a shutter body (10) which can move to and from a closed position in which it prevents the passage of the fluid via this valve, the high-pressure pump (1) further comprising flow regulation means (13) adapted to interfere with the normal operation of the intake valve (9) in order to enable the fluid also to flow freely via the valve in a direction opposite to the normal direction, the high-pressure pump (1) being characterized in that the flow regulation means (13) comprise a hydraulic piston (14) selectively adapted to prevent the shutter body (10) from returning to the closed position.
 2. A high-pressure pump as claimed in claim 1, characterized in that the hydraulic fluid (14) is supplied from the pressurized fluid supplied as input to the intake inlet (1 b) of this pump.
 3. A high-pressure pump as claimed in claim 2, characterized in that the flow regulation means (13) comprise an electrically actuated exhaust valve (15), which is selectively adapted to cause a pressure drop in the fluid that is supplied to the hydraulic piston (14), so as to block the action of this hydraulic piston (14).
 4. A high-pressure pump as claimed in claim 3, characterized in that the flow regulation means (13) comprise an electronic control unit (16) adapted to drive the exhaust valve (15) so as to control the time interval in which the intake valve (9) is disabled.
 5. A high-pressure pump as claimed in claim 1, characterized in that the hydraulic piston (14) is a single-acting hydraulic piston.
 6. A high-pressure pump as claimed in claim 1, characterized in that the intake valve (9) is formed by a non-return valve (9) which comprises an elastic member (12) adapted to maintain the shutter body (10) in the closed position, the hydraulic piston (14) being adapted to prevent the shutter body (10) from returning to its closed position, overcoming the resistance of the elastic member (12).
 7. A system for the supply of fuel to an internal combustion engine, characterized in that it comprises a high-pressure pump (1) as claimed in claim
 1. 